Positive Linear Dispersion in the Velocity of Sound in He II

Abstract

The dispersion in the phase velocity of first sound in He II at 1.38°K was measured between 20 and 60 GHz (1-3°K). The results show direct experimental verification of positive dispersion in the phonon branch. The dispersion in the sound velocity was measured to be $C\left(\nu \right)=C_0[1+(6.3\mathrm{}\pm 0.7)\times {10}^{-13\mathrm{}}\nu +(0\mathrm{}\pm 8)\times {10}^{-25\mathrm{}}{\nu }^2]$.